High voltage niobium oxides and capacitors containing same

ABSTRACT

Nb 1-x Ta x O powder wherein x is 0.1 to 0.5 is described. Further, this powder, as well as niobium suboxide powders, can be doped with at least one dopant oxide. Pressed bodies of the powder, sintered bodies, capacitor anodes, and capacitors are also described.

This application claims the benefit under 35 U.S.C. §119(e) of priorU.S. Provisional Patent Application No. 60/950,450, filed Jul. 18, 2007,which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to niobium oxides, such as niobiumsuboxides, and further relates anodes and capacitors made therefrom.

As described in U.S. Pat. Nos. 6,759,026; 6,639,787; 6,592,740;6,576,099; 6,527,937; 6,462,934; 6,416,730; 6,391,275; 6,373,685; and6,322,912; and U.S. Published Patent Application Nos. 2005/0084445;2004/0040415; 2003/0026756; 2002/0172861; 2002/0135973; 2002/0114722;2001/0036056; 2005/0025699; and 2005/0008564 (all incorporated in theirentirety by reference herein), niobium suboxides have been developedwhich are useful in forming anodes for capacitor applications. Thesepowders, when formed into anodes, can have a capacitance up to about200,000 CV/g or more and can have low DC leakage, for instance, fromabout 0.1 nA/CV to about 5.0 nA/CV. As described in these patents, thetypical formation voltage for these niobium suboxide products, whenformed into an anode, can be from about 6 to about 70 volts andpreferably about 35 volts. These patents describe other high formationvoltages, such as from 70 volts to about 130 volts. While theseabove-described patents describe a balance of properties with respect toDC leakage, capacitance, and formation voltage, as higher formationvoltages are used, typically, the DC leakage increases, which can resultfrom elevated electronic and/or ionic conduction in the dielectric layerat high voltage stresses. High conductivity can be a result ofcontaminants in the powder and a variety of defects generated during theanodization process, such as oxygen vacancies, crystallization, physicaldefects, and the like. Capacitor powder manufacturers have traditionallydealt with this problem by reducing the level of contaminants in thepowder. However, this approach has technical and commercial limitationsdue to the high costs of purifying the materials, as well as othertechnical reasons. Accordingly, it would be highly desirable tostabilize the dielectric layer such that the charge carriers areimmobilized or compensated thereby allowing the ability to form niobiumsuboxide powders at a higher formation voltage and yet preferably obtainlow DC leakage.

SUMMARY OF THE PRESENT INVENTION

A feature of the present invention is to provide niobium suboxidematerials that have anodization constants that can be lowered so thathigher voltage formation is facilitated.

A further feature of the present invention is to achieve higher voltageformation while controlling DC leakage at high voltage formations. Afurther feature of the present invention is to provide powders which canfacilitate high voltage formation.

Additional features and advantages of the present invention will be setforth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a Nb_(1-x)Ta_(x)O, wherein x is0.1 to 0.5.

The present invention further relates to powder comprising theNb_(1-x)Ta_(x)O powder.

Also, the present invention relates to a Nb_(1-x)Ta_(x)O powder that isdoped with at least one dopant oxide.

Furthermore, the present invention relates to sintered pressed bodiescomprising the powder of the present invention and capacitor anodes madetherefrom.

Also, the present invention relates to a niobium suboxide powder havingthe formula Nb_(x)O_(y) that is doped with at least one dopant oxide,wherein x is less than 2 and y is less than 2.5×.

The present invention further relates to sintered pressed bodies andanodes made from this niobium suboxide powder.

Also, the present invention relates to powders, sintered pressed bodies,capacitor anodes, and capacitors having beneficial properties achievedwith the use of one or more powders of the present invention, such asthe ability to form at higher voltage formation and yet achieve stableDC leakage and/or lowering the anodization constant. Other benefits arefurther described.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this application, illustrate some of the embodiments of thepresent invention and together with the description, serve to explainone or more principles of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of two pathways for formation ofhigh voltage Nb suboxide products.

FIGS. 2 and 3 are x-ray diffraction graphs for certain samples of thepresent invention.

FIGS. 4 and 5 are x-ray diffraction graphs for certain samples of thepresent invention.

FIG. 6 a is a graph showing CV/g behavior as a function of formationvoltage for several samples.

FIG. 6 b is a graph showing DC leakage behavior as a function offormation voltage.

FIGS. 7 and 8 are x-ray diffraction graphs for certain samples of thepresent invention.

FIG. 9 is a graph showing DC leakage as a function of Y₂O₃ content inNb_(1-x)Ta_(x)O materials.

FIG. 10 is a graph showing DC leakage as a function of formation voltagefor Nb_(1-x)Ta_(x)O materials.

FIG. 11 is a graph showing DC leakage as a function of formation voltagefor various donor oxide Nb suboxide materials.

FIG. 12 is a graph showing CV/g as a function of formation voltage forvarious doped Nb suboxide materials.

FIG. 13 is a graph showing CV/g as a function of powder BET surface areafor various dopant Nb suboxide materials.

FIG. 14 is a graph showing DCLeakage (at 60V formation) as a function ofmetallic combination (Fe+Ni+Cr).

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In an embodiment of the present invention, the present invention relatesto a Nb_(1-x)Ta_(x)O powder, wherein x is 0.1 to 0.5. For purposes ofthe present invention, the powder can comprise this Nb_(1-x)Ta_(x)Opowder or the Nb_(1-x)Ta_(x)O powder can be present as a majority of theoverall powder present as a layer or as a mixture, for example. TheNb_(1-x)Ta_(x)O powder can be present in amounts up 90% by weight ormore, such as 99% or 99.9% or higher or 100%. The Nb_(1-x)Ta_(x)O powdercan be the primary powder present, wherein any other powder presentwould be considered an impurity. In other words, the powder can consistessentially of or consist of Nb_(1-x)Ta_(x)O powder. As an option, x canbe 0.2 to 0.4 or 0.25 to 0.35 or any other ranges within the range of0.1 to 0.5 (e.g., 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45). TheNb_(1-x)Ta_(x)O powder can be a crystalline Nb_(1-x)Ta_(x)O powderand/or an amorphous Nb_(1-x)Ta_(x)O powder or any mixture or combinationthereof.

Powder physical properties are presented in Tables 4, 8, 12, and 16 thatinclude a BET surface area (1.32-1.81 m²/g), Scott density (20.4-25.9g/in³), and average particle size (d50) as measured by Horiba LA-910light scattering method (without and with 120 s ultrasonication), 80-124μm, and 28-42 μm respectively. The powder of the present invention canhave any one or more of these above properties. The BET surface area canbe from 1 m²/g to 3.0 m²/g or higher, or from 1.2 to 2.5 m²/g, or from1.3 m²/g to 2.2 m²/g or from 1.4 m²/g to 2.0 m²/g. The Scott density canbe from 17 g/in³ to 30 g/in³ or from 18 g/in³ to 28 g/in³ or from 20g/in³ to 28 g/in³. The Scott density can be below or above any of theselimits. The flow can be acceptable flow rates as determined bycommercially acceptable standards for niobium or tantalum powders. Thepowder flow can be measured based on ASTM B 213-97.

The average particle size (d50) without 120 s ultrasonication can befrom 60 to 175 μm or from 65 to 160 μm or from 75 to 150 μm or from 35to 140 μm. The average particle size (d50) with 120 s ultrasonicationcan be from 15 to 60 μm or from 20 to 50 μm or from 25 to 45 μm. Theaverage particle size can be below or above any of these limits. Thepowder of the present invention can have one or more of theseproperties. The powder can be unagglomerated or agglomerated.

In one or more embodiments, the Nb_(1-x)Ta_(x)O powder can be doped withat least one dopant oxide. As an example, the powder can be doped withat least one oxide of Y, Si, Mn, Al, Ce, V, or a combination thereof.Specific examples include, but are not limited to, Y₂O₃, SiO₂, Mn₃O₄,Al₂O₃, Mn₂O₃, CeO₂, or V₂O₃. The powder can be doped with at least onedopant having a cation valancy of +2 or higher (e.g., +3, +4). Thedopant can have an ionic size that is within 10% of the ionic size ofniobium. In other words, the dopant can have an ionic size that is thesame as or larger than or smaller than the ionic size of niobium and canbe, for instance, within 10% of the ionic size of niobium.

The dopant oxide can be present with the Nb_(1-x)Ta_(x)O powder in anyamount. For instance, the amount can be an amount sufficient to lowerthe DC leakage characteristics of the material compared to no dopantoxide being present. The amount of the dopant oxide present can be, forexample, 3% by weight or less based on the overall weight of the powder.For instance, the amount of the dopant oxide can range from 0.25 to 3%by weight, from 0.5 to 2.5% by weight, from 0.5 to 2% by weight, or from0.5 to 1.75% by weight. It is to be understood that these ranges canalso be approximate ranges. Thus, as an option, each range can beunderstood to include the term “about” before each numerical number. Forinstance, 0.25 to 3% by weight can also be, as an option, from about0.25 to about 3% by weight and so on.

The dopant oxide, as an option, can have any purity level. For instance,the purity level of the dopant oxide can be 95% or higher with respectto purity by wt %. Other ranges include 98% purity or higher, 99% purityor higher, 99.5% purity or higher, 99.9% purity or higher, or 99.995%purity or higher. Suitable ranges are from 95% to 99.995% purity orhigher, 98% to 100% purity, and so on.

The dopant oxide can be introduced into the Nb_(1-x)Ta_(x)O powder byany technique, such as by blending the dopant oxide, if present as asolid (e.g., powder) with the Nb_(1-x)Ta_(x)O powder. Preferably, auniform blending is achieved to properly distribute the dopant oxidethroughout the Nb_(1-x)Ta_(x)O powder. Other techniques to dope theNb_(1-x)Ta_(x)O powder include, but are not limited to, the use of agas, liquid, or any combination thereof. The dopant oxide can beintroduced wherein the metal precursor of the dopant oxide is introducedand then oxidized to form the dopant oxide. Dopants can also be appliedas surface coatings on the separate, blended, or comilled substrateparticles. Coatings can be applied via precipitation of a dopant oxidefrom a liquid dopant precursor in the presence of substrate particles,or by evaporating (drying) a mixture of substrate particles and liquiddopant precursor. Alternatively, dopants can be applied to NbO orNb_(1-x)Ta_(x)O powders during capacitor anode fabrication prior tosintering.

In one or more embodiments of the present invention, the presentinvention further includes forming a pressed body from the powder of thepresent invention. This pressed body can be a green body. Also, thepressed body can be sintered to form a sintered anode or capacitor anodeusing conventional techniques of pressing, sintering, and the like.Further, the capacitor anode can be included as a component to form acapacitor (e.g., wet or dry solid capacitors). Also, the capacitor anodecan have a dielectric layer formed on the capacitor anode. Any pressdensity can be used in forming the pressed body of powder. For instance,the press density can be 3.0 g/cc or higher. For instance, the pressdensity can be from 3.0 g/cc to 3.75 g/cc. The press density can be 3.1g/cc or 3.2 g/cc or 3.3 g/cc, which is especially useful in high voltageformation capacitor anodes. For instance, the press density can beuseful for capacitor anodes formed at a formation voltage of 60 volts to75 volts with a capacitance of 60,000 to 75,000 CV/g. The capacitoranodes of the present invention can be incorporated in capacitor designshaving A, B, C, and D case sizes.

In one or more embodiments of the present invention, the sintered anodefrom the Nb_(1-x)Ta_(x)O powder can have a cumulative volume of poresgreater than 1 micron diameter (e.g., 1.1 micron to 10 microns), whichcan be maintained at 0.010 mL/g or greater levels (such as 0.050 mL/g toabout 0.1 mL/g, or 0.025 mL/g to about 0.07 mL/g), even at higher pressdensities, such as 3.0 g/cc or higher, including the ranges describedabove with respect to press densities. These pore volumes are sufficientfor cathode impregnation in forming the capacitor. Further, thesesintered anode pore volumes can be achieved along with a capacitor anodehaving desirable capacitance, such as from 50,000 CV/g to 75,000 CV/g orhigher with a formation voltage of from 60 volts to 75 volts.

Nb_(1-x)Ta_(x)O powder doped with an oxide of Si or an oxide of Mn, suchas SiO₂ and/or Mn₂O₃ were most favorable in obtaining lower DC leakageat all press densities and sintering temperatures.

The dopant oxide can have any physical and chemical characteristics. Forexample, the dopant oxide can have a variety of different surface areasthat can be used. The surface area of the dopant oxide can be withrespect to BET surface area, from about 0.1 to about 500 m²/g, such asfrom about 1 to about 50 m²/g or 3 to 25 m²/g.

The dopant oxides can have the ability to suppress the negative effectsof metal contamination on DC leakage. More particularly, the dopantoxides can suppress the effect of impure Nb metal, if the Nb metal hasimpurities present. With the use of dopant oxides, the purity ofNb_(1-x)Ta_(x)O powder or the niobium suboxide powder having the formulaNb_(x)O_(y) can be from about 99 wt % to about 90 wt % with respect topurity of the Nb suboxide, and preferably obtain comparable lower DCleakage as if a Nb_(x)O_(y) or Nb_(1-x)Ta_(x)O material has a purity of99.9 wt % is used.

In one or more embodiments of the present invention, anodes formed fromthe Nb_(1-x)Ta_(x)O powder can have a DC leakage of less than about 5.0nA/CV, such as from about 0.10 nA/CV to 4.5 nA/CV. Further, the anodecan have a capacitance of from 50,000 CV/g to 75,000 CV/g or higherbased on a voltage formation of 60 volts to 75 volts with a formationtemperature of 90° C. and wherein the capacitor anodes are formed with apressed density of 3.0 g/cc to 3.5 g/cc, and wherein the anode issintered at a temperature of from 1200° C. to 1750° C. (such as from1200° C. to 1400° C. or 1350° C.) for 10 minutes. The sintering time canbe lower or higher. For purposes of the present invention, all recitedcapacitances are based on the above test standards.

In one or more embodiments of the present invention, once a dielectriclayer is formed on the capacitor anode of the present invention, usingmicroscopic analysis, no field-induced crystallization within thedielectric layer occurs. Thus, in one or more embodiments of the presentinvention, the present invention relates to a capacitor anode made fromNb_(1-x)Ta_(x)O powder or powder containing the same with a dielectriclayer formed on the capacitor anode (e.g., Nb₂O₅) and wherein thedielectric layer does not have any field-induced crystallization withinthe dielectric layer. The lack of any field-induced crystallizationwithin the dielectric layer can be present with any of the anodes of thepresent invention including anodes formed at a formation voltage of from60 volts to 75 volts or higher and, optionally, with the DC leakageand/or capacitance ranges provided above.

In one or more embodiments of the present invention, the capacitor anodeformed from the Nb_(1-x)Ta_(x)O powder can have no or minimal amounts ofTa₂O₅ present in the powder. For instance, preferably no Ta₂O₅ ispresent in the anode of the present invention. The capacitor anode ofthe present invention can have trace amounts of Ta₂O₅ present in thecapacitor anode, such as from about 0.01 wt % to about 5.0 wt % or fromabout 0.1 wt % to about 0.5 wt %. The Ta₂O₅ can be with respect tocrystalline Ta₂O₅, which can be present as a crystalline Ta₂O₅ phase inthe powder.

In preparing the Nb_(1-x)Ta_(x)O powder, it can be prepared, forinstance, using tantalum oxides or tantalum hydroxides along withniobium hydroxides or niobium oxides. Using a process similar to theprocess described in the above-identified patents, these feed materialscan be optionally calcined to transform them to tantalum oxide orniobium oxide if the starting material was not an oxide to begin with.These materials can then be mixed with niobium or NbH and subjected toheat treatment(s) to obtain the Nb_(1-x)Ta_(x)O powder. The heattreatment(s) can be at any temperature sufficient to convert the feedmaterials to the Nb_(1-x)Ta_(x)O powder, such as from 800° C. to 1400°C., in vacuum, for 1 hour to 4 hours or more. Other heat treatment timescan be used. Depending upon the particular powder desired, this willcontrol the amount of niobium and tantalum feed materials, as shown inthe examples, for instance.

With respect to the feed materials, preferably the particle size of thefeed materials is from about 0.05 μm to about 10 μm, such as from about1.0 μm to about 5.0 μm. Other sizes can be used.

In another embodiment of the present invention, the present inventionrelates to a niobium suboxide powder having the formula Nb_(x)O_(y) thatis doped with at least one dopant oxide, wherein x is less than 2 and yis less than 2.5×. Typical reduced niobium oxides comprise NbO,NbO_(0.7), NbO_(1.1), NbO₂, and any combination thereof with or withoutother oxides present. Generally, the reduced niobium oxide of thepresent invention has an atomic ratio of niobium to oxygen of about1:less than 2, such as 1:1.1, 1:1, or 1:0.7. Put another way, thereduced niobium oxide preferably has the formula Nb_(x)O_(y), wherein Nbis niobium, x is 2 or less, and y is less than 2.5×. As examples, x canbe 1 and y can be less than 2, such as 1.1, 1.0, 0.7, and the like. Thedopant oxides and the other characteristics of the dopant oxides withrespect to amounts, examples, and the like are the same as describedabove. Similar advantages are achieved in this embodiment with respectto lowering the anodization constant, the ability to form at highervoltages as described above, and the ability to stabilize or improve DCleakage as described above. Thus, the various property characteristicsof the powder, the pressed body, the sintered pressed body, thecapacitor anode, and the capacitor formed therefrom as described aboveare incorporated in their entirety in this embodiment as well.

In either embodiment the anodization constant can be from about 1.5 nm/Vto about 3.5 nm/V, such as from about 2.0 nm/v to about 3.0 nm/V.

FIG. 1 provides a schematic representation of the various formationpathways for the embodiments of the present invention.

The method can include the steps of heat treating a starting niobiumoxide (or precursor) with the tantalum oxide (or precursor) in thepresence of a getter material (e.g., niobium) in an atmosphere whichpermits the transfer of oxygen atoms from the niobium oxide (and/ortantalum oxide) to the getter material for a sufficient time and at asufficient temperature to form an oxygen reduced niobium-tantalum oxide.

For purposes of the present invention, the niobium oxide can be at leastone oxide of niobium metal and/or alloys thereof. A specific example ofa starting niobium oxide is Nb₂O₅.

The niobium oxide (or precursor) and/or tantalum oxide (or precursor)used in the present invention can be in any shape or size. Preferably,the niobium oxide (or precursor) and/or tantalum oxide (or precursor) isin the form of a powder or a plurality of particles. Examples of thetype of powder that can be used include, but are not limited to, flaked,angular, nodular, and mixtures or variations thereof. Preferably, theniobium oxide and/or tantalum oxide is in the form of a powder whichmore effectively leads to the oxygen reduced niobium-tantalum oxide.Examples of such preferred powders include those having mesh sizes offrom about 60/100 to about 100/325 mesh and from about 60/100 to about200/325 mesh. Another range of size is from −40 mesh to about −400 mesh.

The getter material for purposes of the present invention is anymaterial capable of reducing the specific starting niobium oxide to theoxygen reduced niobium oxide. Preferably, the getter material comprisestantalum, niobium, or both. Other getter materials can be used or incombination with the tantalum or niobium getter materials. Also, othermaterials can form a part of the getter material. The getter materialcan be in any shape or size. The getter materials can be in the form ofa powder in order to have the most efficient surface area for reducingthe niobium oxide. The getter material, thus, can be flaked, angular,nodular, and mixtures or variations thereof. Generally, a sufficientamount of getter material is present to at least partially reduce theniobium oxide being heat treated. Further, the amount of the gettermaterial is dependent upon the amount of reducing desired to the niobiumoxide. In one or more embodiments of the present invention, the processdoes not require the use of a sacrificial getter. Both oxide (Nb₂O₅and/or Ta₂O₅) and getter component (NbH) can be comilled together toform the suboxide materials and ultimately form the target composition.

The heat treating that the starting niobium oxide (or precursor) and/ortantalum oxide (or precursor) is subjected to can be conducted in anyheat treatment device or furnace commonly used in the heat treatment ofmetals, such as niobium and tantalum. The heat treatment of the niobiumoxide (or precursor) and/or tantalum oxide (or precursor) in thepresence of the getter material is at a sufficient temperature and for asufficient time to form an oxygen reduced niobium-tantalum oxide. Thetemperature and time of the heat treatment can be dependent on a varietyof factors such as the amount of reduction of the niobium oxide, theamount of the getter material, and the type of getter material as wellas the type of starting niobium oxide (or precursor) and/or tantalumoxide (or precursor). Generally, the heat treatment of the niobium oxidewill be at a temperature of from less than or about 800° C. to about1900° C. and more preferably from about 1000° C. to about 1500° C., andmost preferably from about 1250° C. to about 1350° C. The heat treatmentis performed for a time of from about 5 minutes to about 100 minutes,such as from about 30 minutes to about 60 minutes. Routine testing inview of the present application will permit one skilled in the art toreadily control the times and temperatures of the heat treatment inorder to obtain the proper or desired reduction of the starting niobiumoxide or tantalum oxide. The heat treatment occurs in an atmospherewhich permits the transfer of oxygen atoms from the niobium oxide to thegetter material. The heat treatment can occur in a hydrogen containingatmosphere which is preferably just hydrogen or in vacuum. Other gasescan be used or can also be present with the hydrogen, such as inertgases, so long as the other gases do not react with the hydrogen. Thehydrogen atmosphere during the heat treatment can be at a pressure offrom about 10 Torr to about 2000 Torr, and more preferably from about100 Torr to about 1000 Torr, and most preferably from about 100 Torr toabout 930 Torr. Mixtures of H₂ and an inert gas such as Ar can be used.Also, H₂ in N₂ can be used to effect control of the N₂ level of theniobium oxide. During the heat treatment process, a constant beattreatment temperature can be used during the entire beat treatingprocess or variations in temperature or temperature steps can be used.

The oxygen reduced niobium-tantalum oxides can also contain levels ofnitrogen, e.g., from about 100 ppm to about 80,000 ppm N₂ or to about130,000 ppm N₂. Suitable ranges includes from about 1,000 ppm N₂ toabout 50,000 ppm N₂ and from about 5,000 ppm N₂ to about 15,000 N₂.

The present invention also relates to a capacitor anode in accordancewith the present invention having a niobium oxide film or other metaloxide film on the surface of the capacitor. The anode can be part of anelectrolytic capacitor. The anode can be a solid electrolytic anode orcan be a wet anode. Preferably, the film is a niobium pentoxide film.The means of making metal powder into capacitor anodes and variouscapacitor designs are known to those skilled in the art and can be usedherein, such as those set forth in U.S. Pat. Nos. 4,805,074, 5,412,533,5,211,741, and 5,245,514, and European Application Nos. 0 634 762 A1 and0 634 761 A1, all of which are incorporated in their entirety herein byreference.

The capacitors of the present invention can be used in a variety of enduses such as automotive electronics, cellular phones, computers, such asmonitors, mother boards, and the like, consumer electronics includingTVs and CRTs, printers/copiers, power supplies, modems, computernotebooks, disc drives, and the like.

The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES Example 1

The following experimental and evaluation methods were used in theexamples:

Calcination of Nb and Ta Oxides: As-received Ta(OH)₅ or Nb(OH)₅ sampleswere calcined to obtain feed materials (for making NbO based materialsusing a comilling process as described in U.S. Published PatentApplication No. 2005/0025699, incorporated in its entirety by referenceherein) with desired particle size and BET surface area. Ta(OH)₅ andNb(OH)₅ were transformed to corresponding oxides (Ta₂O₅, and Nb₂O₅) uponcalcination. The calcination occurred in a lab scale muffle furnace(Thermolyne, electric resistance) at a 40-60 g size, using a porcelaincrucible. Larger scale calcinations (2-16 kg size) were carried out inthe pilot scale electric muffle furnace, using Amersil quartz boats. Allcalcined materials were screened with 50 mesh, using Sweco vibratoryscreener before testing for BET surface area.

Preparation of SG Grade NbH: Multiple Lots of NbH were Prepared byAttritor milling NbH in water. Metallurgical grade Nb ingot slices werehydrided and jaw crushed to below 40 mesh particle size grade, followedby coarse wet (in presence of water) grinding in Union Process 5Sattritor mill using 3/16″ diameter spherical Nb media for about 6 hours.The coarse ground NbH material was then milled again with 1/16″ media toproduce SG grade NbH. Both 1S and 5S size mills were used with 1/16″size Nb spherical media, running at 410 and 190 RPM, respectively.Typical batch size in 1S mill was about 4 kg, while 5S mill generatedlots of 16-20 kg size. Milling time ranged between 20-25 h, for a targetBET surface area of 3.8 m²/g. At the end of milling, the slurry wassampled for Horiba particle size analysis and allowed to sit overnightfor settling, followed by decanting to obtain a sediment ofapproximately 50% in solids. The sediment was dried under vacuum at 12°C., followed by screening with 50 mesh to create powder. The finalpowder was tested for BET surface area, oxygen and hydrogen.

Comilling of NbH and Ta₂O₅/Nb₂O₅: Calcined and screened Nb₂O₅ and Ta₂O₅materials were hand mixed with NbH powder (˜3.5 m²/g) in appropriatemole proportions, as specified for each sample. For samples with Y₂O₃doping, commercially available Y₂O₃ nanopowder (25-30 nm, 40-45 m²/g,sigma-aldrich.com) was also added to this mixture. The mixture was thenloaded into 01HD attritor mill. Operating conditions for comilling arelisted in Table 3. At the end of milling, the slurry was sampled forHoriba particle size analysis and allowed to sit overnight for settling,followed by decanting to obtain a sediment of approximately 50% insolids. The sediment was dried under vacuum at 120C, followed bypassivation to obtain a dry cake.

Green screening: Dried comilled mixture was screened to a final maximumgranule size (−140 mesh/106 μm), using a SWECO shaker. The powder wasscreened through a fine mesh in order to lower the bulk density of thefinal NbO powder to the desired range of 1.1-1.2 g/cc. The finalscreening step was preceded by a rough 20 mesh and a medium 50 meshscreening steps to avoid excessive damage and screen clogging typicallyassociated with one step screening. The screened product was tested forBET surface area, bulk density, and Horiba particle size distribution.

Conversion to Nb_(x)O_(y) or Nb_(1-x)Ta_(x)O: The screened granularmixture was converted to Nb_(x)O_(y) or Nb_(1-x)Ta_(x)O by heat treatingat 1350-1375C in vacuum for 4 h, followed by a reaction step @ 850C inhydrogen (2 psig) for 1 hour. A heat treatment step was used to hardenthe granules sufficiently, so that the product has good flow in powderform, and pore structure in the sintered anode form. All samples havebeen heat treated at ˜50 g size, placed in a 3″ alumina crucible.Alumina crucibles were placed inside a 8″×10″ Mo tray.

Characterization of Nb_(x)O_(y) or Nb_(1-x)Ta_(x)O: Following the heattreatment and reaction process, the Nb_(x)O_(y) or Nb_(1-x)Ta_(x)Osamples were screened with 50 mesh to breakup any lumps and remove largeagglomerates. The samples were then evaluated for flow, bulk (Scott)density, HORIBA particle size analysis with a 0-2 min sonication time,and wet electrical (CV/g, and DC Leakage at 180 s) evaluation on anodeswith 2.8-3.5 g/cc pressed green density followed by sintering at 1380°C. for 10 min. Formation voltage ranged between 30 and 60V. Green crushstrength was also evaluated on the pressed anodes. Physical propertiesof sintered anodes, such as sinter density, and diameter shrinkage, werealso measured. XRD analysis was performed at Micron, Inc., using 0.5degree/min scan rate between 20-45° degrees 2-theta.

Experimental design, raw materials and processing data, andcharacterization data for Nb_(1-x)Ta_(x)O samples are shown in Tables1-4.

TABLE 1 Experimental design for Nb_(1−x)Ta_(x)O NbO Nb_(1−x) Ta_(x)O_(y) M/O Sample Target Target Target Target A 0.88 0.12 0.98 1.02 B0.74 0.26 0.98 1.02 C 0.66 0.34 0.98 1.02 D 1.00 0.00 0.98 1.02

TABLE 2 Raw material information for Nb_(1−x)Ta_(x)O NbH Feed Nb₂O₅ FeedTa₂O₅ Feed NbO Wt Wt Wt Sample Type (g) Type (BET) (g) Type (BET) (g) ASG 291 F&X-1.60 m²/g 134 DLS-1.00 m²/g 125 B SG 264 F&X-1.60 m²/g 46DLS-1.00 m²/g 240 C SG 250 F&X-1.60 m²/g 0 DLS-1.00 m²/g 300 D SG 319F&X-1.60 m²/g 231 DLS-1.00 m²/g 0 F&X - Commerical Supplier of Nb(OH)₅that was calcined to Nb₂O₅ to target BET. DLS - Commercial Supplier ofTa(OH)₅ that was calcined to Ta₂O₅ to target BET. Similar notations inTables are used.

TABLE 3 Milling conditions and green milled mixture properties for thefour samples made using 01HD attritor mill (500 g batch size) as part ofNb_(1−x)Ta_(x)O examples 01HD Attritor Mill Milled Slurry Green ScreenedCornilling Conditions Properties Screening Granule HD01 Media SpeedD50-60s US BET Mesh Bulk Density Sample (INCH) Time (min) RPM (μm)(m²/g) ASTM (g/in³) A 1/16 120 700 1.07 4.93 −140 15.7 B 1/16 120 7001.02 4.64 −140 17.8 C 1/16 120 700 0.97 4.29 −140 19.2 D 1/16 120 7001.10 5.07 −140 13.6 D50-60s US = D50 size after 60 seconds ofultrasonication (US). Similar notations in Tables are used.

TABLE 4 Table 4. Post-reaction characterization data for the foursamples made as part of Nb_(1−x)Ta_(x)O study. All samples have beenheat treated at 1350 C. for 240 min., followed by reaction in positiveH₂ atmosphere (860 Torr) at 850 C. for 60 min., in MRF furnace LF2. ~50g of each sample, placed in a 3″ alumina crucible. HORIBA PSD (μm)Powder SCOTT (LA-910) ANODE Green Wet Electricals @ 30V_(f) SinterSinter Sam- Nb_(1−x)Ta_(x)O BET Density D90 D50 D50 dP CRUSH Vbias CV/gDCL @ 180s Density Shrinkage ple X= (m²/g) (g/in³) (0s US) (0s US) (120sUS) (g/cc) (LB) (V) (μF · V/g) (nA/CV) (g/cc) (% Dia) D 0.00 1.37 20.7147 81 36 2.80 1.9 2.5 112858 0.23 2.99 0.92 10 90023 0.29 A 0.12 1.7821.4 272 90 37 2.80 1.9 2.5 146661 3.91 2.92 0.07 10 105790 5.42 B 0.261.80 21.1 147 — 31 2.80 1.3 2.5 139108 7.80 2.85 −0.49 10 97158 11.173.10 1.2 2.5 135470 6.28 3.14 −0.76 10 95227 8.94 C 0.34 1.78 25.2 14479 35 2.80 1.0 2.5 140525 10.32 2.85 −0.36 10 100563 14.43 3.10 1.6 2.5140950 7.78 3.16 −0.74 10 102041 10.75 3.50 5.6 2.5 138415 8.20 3.52−0.83 10 101542 11.17 0s = no sonication 120s US = 120s ofultrasonication

The powder flow rate was acceptable for capacitor grade powders. Thebulk density of screened granules gradually increased with increasing Taconcentration.

Physical properties of heat treated and reacted samples listed in Table4 show that the BET surface area of Nb_(1-x)Ta_(x)O type samples issignificantly higher than the control (pure NbO) sample.

X-ray diffraction data for the heat treated and reacted samples is shownin FIGS. 2 and 3. It is worth noting that major peaks in the XRD patternfor all samples correspond to a pure NbO pattern. This indicates that Tasubstitution into the primary NbO lattice has been successful, includingthe Ta mole fraction of 0.34 used in this experiment. Minor peak(additional phases) analysis show the presence of trace amounts ofunreacted Ta₂O₅ in all Nb_(1-x)Ta_(x)O type samples. This is a switchfrom NbO₂ minor phase typically seen in pure NbO samples, indicatingthat Ta₂O₅ is preferentially more stable compared to NbO₂.

Example 2

Analysis of Y₂O₃-doped Samples. Experimental design, raw materials andprocessing data, and characterization data for Y₂O₃-doped NbO samplesare shown in Tables 5-8.

TABLE 5 Experimental design for Y₂O₃-doped NbO study NbO Y₂O₃ Nb/O Lot #wt % Amount (g) Mole Ratio E 0.00 0.00 1.030 F 1.00 5.00 1.030 G 3.0015.00 1.030

TABLE 6 Raw material information for Y₂O₃-doped NbO study Y₂O₃ NbO NbHFeed Nb₂O₅ Feed Amount Lot # Type Wt (g) Type Wt (g) wt % (g) E SG 292Duoloshan-1.7 m²/g 208 0.00 0.00 F SG 292 Conghua-1.4 m²/g 208 1.00 5.00G SG 292 Conghua-1.4 m²/g 208 3.00 15.00 Conghua and Duoloshan arecommercial suppliers of the hydroxide that was calcined to the targetBET.

TABLE 7 Milling conditions and green milled mixture properties for thethree samples made using 01HD attritor mill (500 g batch size) as partof Y₂O₃-doped NbO study 01HD Attritor Mill Milled Slurry Green ScreenedCornilling Conditions Properties Screening Granule HD01 Media SpeedD50-60s US BET Mesh Bulk Density Sample (INCH) Time (min) RPM (μm)(m²/g) ASTM (g/in³) E 1/16 100 700 1.05 5.07 −140 13.8 F 1/16 135 7001.06 6.09 −140 14.7 G 1/16 135 700 1.02 5.80 −140 17.5

TABLE 8 Table 8. Post-reaction characterization data for the threesamples made as part of Y₂O₃- doped NbO study. All samples have beenheat treated at 1375 C. for 240 min., followed by reaction in positiveH₂ atmosphere (860 Torr) at 850 C. for 60 min., in furnace LF2. ~50 g ofeach sample, placed in a 3″ alumina crucible. HORIBA PSD (μm) Y₂O₃Powder SCOTT (LA-910) ANODE Green Wet Electricals @ 30V_(f) SinterSinter Added BET Density D90 D50 D50 dP CRUSH Vbias CV/g DCL @ 180sDensity Shrinkage Sample (wt %) (m²/g) (g/in³) (0s US) (0s US) (120s US)(g/cc) (LB) (V) (μF · V/g) (nA/CV) (g/cc) (% Dia) E 0.0 1.37 20.8 144 8032 2.8 1.12 2.5 108638 0.10 3.02 1.12 10 85269 0.13 F 1.0 1.64 20.2 12977 28 2.8 1.38 2.5 122076 0.11 3.08 2.06 10 92519 0.14 G 3.0 1.48 23.2145 85 34 2.8 0.28 2.5 88406 0.12 2.93 0.68 10 67620 0.16

The powder flow rate was acceptable for capacitor grade powders.Observation of milled mixture properties showed a gradual increase inbulk density of screened granules with increasing Y₂O₃ concentration.This was probably due to the fact that milled slurries of Y₂O₃ dopedsamples were very stable (minimal settling with time) leading to theformation of a tightly packed sediment during drying. The BET surfacearea of milled mixtures was higher for Y₂O₃ doped samples, owing to thenanoscale particle size of Y₂O₃ powder used.

Electrical characteristics shown in Table 8 indicate that at 3 wt %Y₂O₃, CV/g is adversely effected, very likely due to the lowereddielectric constant triggered by the excessive substitution of Y ion inNbO lattice. In addition, physical characteristics are also adverselyaffected at 3 wt % Y₂O₃ (high Scott density and low crush strength).X-ray diffraction data shown in FIGS. 4 and 5 also confirms thesignificant change in structure of 3 wt % Y₂O₃ doped NbO (shift in majorpeak positions). However, at 1 wt % Y₂O₃, the material appears to behavevery similar to control (pure NbO) sample, in both physical andelectrical characteristics. Unlike Nb_(1-x)Ta_(x)O type samplesdescribed earlier, the anode color after formation is not significantlydifferent than the pure NbO control samples, indicating that theanodization constant was not affected by Y₂O₃ doping.

Additional testing was done at higher formation voltages to evaluate theDC leakage characteristics of Y₂O₃-doped samples. The data from thesetests are graphically shown in FIGS. 6 a and 6 b. As evident from thisdata, 1 wt % Y₂O₃ doped sample showed significantly lower DC leakage athigher formation voltages. However, as also shown in FIG. 6 a, theanodization constant remains more or less unchanged, therefore CV/gdrops precipitously beyond 45V formation. At 45V formation, 1 wt % Y₂O₃doped NbO appears to provide a viable dielectric layer with reasonableCV/g.

Example 3

Experimental design, raw materials and processing data, andcharacterization data for Y₂O₃ doped Nb_(1-x)Ta_(x)O samples are shownin Tables 9-12. The milled particle size gradually decreased withaddition of Y₂O₃ nanopowder. Higher granule bulk density (compared topure NbO materials) is expected from heavier Ta substitution in thesematerials and remained roughly constant among all three samples.

TABLE 9 Experimental design for Y₂O₃ doped Nb_(1−x)Ta_(x)O study BatchTa_(x) Donor Oxide NbO Size Nb_(1−x) Tar- O_(y) N/O Amount Lot # (g)Target get Target Target Type wt % (g) H 575 0.61 0.39 0.94 1.06 — 0.000.00 I 575 0.61 0.39 0.94 1.06 Y203 1.00 5.75 J 575 0.61 0.39 0.94 1.06Y203 2.00 11.50

TABLE 10 Raw material information for Y₂O₃ doped Nb_(1−x)Ta_(x)O studyNbO NbH Feed Ta₂O₅ Feed Ta Feed Donor Oxide Lot # Type Wt (g) Type Wt(g) Type Wt (g) Type wt % Amount (g) H SG 235 DLS-1.00 m²/g 300HP500-DB-B 40 — 0.00 0.00 I SG 235 DLS-1.00 m²/g 300 HP500-DB-B 40 Y2031.00 5.75 J SG 235 DLS-1.00 m²/g 300 HP500-DB-B 40 Y203 2.00 11.50 Tafeed: Basic Lot of C-515 Ta from Cabot Corporation

TABLE 11 Milling conditions and green milled mixture properties for thethree samples made using 01HD attritor mill (500 g batch size) as partof Y₂O₃ doped Nb_(1−x)Ta_(x)O study 01HD Attritor Mill Milled SlurryGreen Screened Cornilling Conditions Properties Screening Granule HD01Media Speed D50-60s US BET Mesh Bulk Density CM Lot # (INCH) Time (min)RPM (μm) (m²/g) ASTM (g/in³) H 1/16 120 700 1.30 3.81 −140 19.6 I 1/16120 700 1.06 4.20 −140 20.0 J 1/16 120 700 0.96 3.84 −140 19.7

TABLE 12 Table 12. Post-reaction characterization data for the threesamples made as part of Y₂O₃ doped Nb_(1−x)Ta_(x)O study. All sampleshave been heat treated at 1350 C. for 270 min., followed by reaction inpositive H₂ atmosphere (860 Torr) at 850 C. for 60 min., in MRF furnaceLF2. ~50 g of each sample, placed in a 3″ alumina crucible. Powder SCOTTHORIBA PSD (μm) DCL DCL Sinter Sinter BET Density D90 D50 D50 Vf Vb CV/g@ 180s @ 180s Density Shrinkage TEXT_ID (m²/g) (g/in³) (0s US) (0s US)(120s US) (V) (V) (μF · V/g) (nA/CV) (μA/g) (g/cc) (% Dia) H 1.54 25.9220 105 42 20 10 81173 2.7 266.3 2.86 −0.36 30 10 87145 16.7 1450.6 2.85−0.36 45 10 — — — — — I 1.81 25.7 163 86 31 30 10 86573 2.0 174.6 2.89−0.45 45 10 565 109.5 61.9 2.89 −0.45 60 10 37 2449.6 91.2 2.89 −0.45 J1.73 25.4 213 99 32 30 10 86010 0.5 42.7 2.91 −0.15 45 10 581 51.5 29.92.92 −0.15 60 10 14 5306.3 72.1 2.90 −0.15

As evident from the data listed in Table 12, the final powder BETsurface area (after the heat treatment and reaction) is consistent withmilled mixture BET data discussed above. In general, the surface areavalues indicate fine particle size compared to a typical 80 k CV/g pureNbO powder (typically ranges between 1.2-1.4 m²/g). Ta substitution inNbO appears to hinder sintering kinetics and particle growth during heattreatment process, leading to finer particle size.

From observing the electrical characteristics (also listed in Table 12),the fine particle size of these materials has led to a rapid decline inCV/g at high formation voltages (45V and 60V). However, Y₂O₃ additionhas improved DC leakage characteristics tremendously. The undopedNb_(1-x)Ta_(x)O sample (Sample H) showed very high leakage. The samplewith 2 wt % Y₂O₃ addition (Sample J) has acceptable DC leakage. Both 1wt % and 2 wt % Y₂O₃ doped samples could be formed up to 60V. This is aremarkable improvement in overall applicability of this type ofmaterial.

To further discuss the effect of Y₂O₃ addition on DC leakage behavior ofNb_(1-x)Ta_(x)O type materials, XRD data on three samples of this studyis shown FIGS. 7 and 8. As mentioned earlier, TEM analysis of theNb_(1-x)Ta_(x)O materials (undoped) in some previous samples showedinclusions of crystalline Ta₂O₅ phase in the anodized layer, which isbelieved to be one of the reasons for the high DC leakage of thesematerials. The XRD diffraction data on these powders showed detectablelevels of crystalline Ta₂O₅. As seen in FIGS. 7 and 8, addition of Y₂O₃has gradually and significantly reduced the level of residualcrystalline Ta₂O₅ after heat treatment and reaction. The concurrentreduction DC leakage of these materials with Y₂O₃ addition (FIGS. 9 and10) may indicate a strong relationship between crystalline Ta₂O₅ and DCleakage. In addition, there may be other mechanisms (besides loweredcrystalline Ta₂O₅ in anodized layer) such as donor compensation by whichY₂O₃ acts to lower DC leakage as seen in doped NbO work.

Example 4

Additional Dopants in NbO: Experimental design, raw materials andprocessing data, and characterization data for donor oxide doped NbOsamples are shown in Tables 13-16. Milled mixture properties aregenerally in the expected range for pure NbO type materials, with theexception of very high BET surface area of SiO₂ added sample (CM532).Nanosized fume silica source (Table 13), combined with lower density ofSiO₂ has very likely contributed to the spike in BET and no otherprocess variations are suspected. The reasons for higher than normalgreen granule bulk density for samples CM522 and CM532 are unknown,however, the Scott densities of heat treated samples from these lots arein the normal range (Table 16).

TABLE 13 Experimental design for the study of additional dopant oxidesin NbO. Quantity Donor Source Catalog # Description (g) Oxide Y₂O₃Sigma-Aldrich* 544892-25G Yttrium(III) Oxide 25 Nanopowder, 25-30 nm,40-45 m²/g SiO₂ Sigma-Aldrich* 637238-50G Silica Nanopowder, 99.5%, 5015 nm, 140-180 m²/g Al₂O₃ Sigma-Aldrich* 544833-50G Aluminum Oxide,40-47 nm, 50 gamma phase Mn₂O₃ Sigma-Aldrich* 377457-250G Manganese(III) Oxide, 250 99%, −325 mesh V₂O₃ Sigma-Aldrich* 215988-100G Vanadium(III) Oxide, 98% 100 CeO₂ Sigma-Aldrich* 544841-25G Cerium (IV) Oxide,25 10-20 nm, 80-100 m²/g NbO Batch Nb_(1−x) Ta_(x) O_(y) M/O Donor OxideLot # Size (g) Target Target Target Target Type wt % Amount (g) K 5001.00 0.00 0.97 1.03 Y203 2.00 10.00 L 500 1.00 0.00 0.97 1.03 SiO2 2.0010.00 M 500 1.00 0.00 0.97 1.03 Al2O3 2.00 10.00 N 500 1.00 0.00 0.971.03 MnO2 2.00 10.00 O 500 1.00 0.00 0.97 1.03 V2O3 2.00 10.00 P 5001.00 0.00 0.97 1.03 Ce2O3 2.00 10.00 *Sigma-Aldrich, Inc., 1001 W. St.Paul Avenue, Milwaukee, WI 53233 USA

TABLE 14 Raw material information for the study of additional dopantoxides in NbO. NbH Feed Nb₂O₅ Feed Donor Oxide NbO Wt Wt Amount SampleType (g) Type (g) Type wt % (g) K SG 290 F&X-1.60 m²/g 210 Y2O3 2.0010.00 L SG 290 F&X-1.60 m²/g 210 SiO2 2.00 10.00 M SG 290 F&X-1.60 m²/g210 Al2O3 2.00 10.00 N SG 290 F&X-1.60 m²/g 210 MnO2 2.00 10.00 O SG 290F&X-1.60 m²/g 210 V2O3 2.00 10.00 P SG 290 F&X-1.60 m²/g 210 Ce2O3 2.0010.00

TABLE 15 Milling conditions and green milled mixture properties for thesix samples made using 01HD attritor mill (500 g batch size) as part ofthe study of additional dopant oxides in NbO. 01HD Attritor Mill MilledSlurry Green Screened Cornilling Conditions Properties Screening GranuleHD01 Media Speed D50-60s US BET Mesh Bulk Density Sample (INCH) Time(min) RPM (μm) (m²/g) ASTM (g/in³) K 1/16 120 700 1.06 6.23 −140 16.9 L1/16 120 700 0.98 13.47 −140 16.5 M 1/16 120 700 1.03 5.88 −140 13.6 N1/16 120 700 0.97 5.86 −140 13.1 O 1/16 120 700 1.03 5.67 −140 13.4 P1/16 120 700 1.04 6.15 −140 13.5

TABLE 16 Table 16. Post-reaction characterization data for the sixsamples made as part of the study of additional dopant oxides in NbO.All samples have been heat treated at 1350 C. for 270 min., followed byreaction in positive H₂ atmosphere (860 Torr) at 850 C. for 60 min., inMRF furnace LF2. ~50 g of each sample, placed in a 3″ alumina crucible.Data for control and standard samples is also shown for comparison.Powder SCOTT HORIBA PSD (Lm) DCL DCL Sinter Sinter BET Density D90 D50D50 Vf Vb CV/g @ 180s @ 180s Density Shrinkage SAMPLE (m²/g) (g/in³) (0sUS) (0s US) (120s US) (V) (V) (μF · V/g) (nA/CV) (μA/g) (g/cc) (% Dia) K1.75 22.2 214 112 34 30 10 79624 0.19 15.01 2.94 0.21 45 10 62489 0.5232.39 2.94 0.21 60 10 — — 32.00 2.94 0.21 L 1.52 21.1 154 89 34 30 1089687 0.14 12.39 2.97 0.31 45 10 81563 0.19 15.49 2.97 0.31 60 10 189760.80 15.09 2.97 0.31 M 1.72 21.2 158 92 40 30 10 91501 0.23 21.03 2.990.31 45 10 83168 0.39 32.33 2.97 0.31 60 10 385 67.44 25.96 2.97 0.31 N1.32 22.5 158 91 41 30 10 84271 0.14 12.01 2.96 0.52 45 10 81977 0.2016.14 2.97 0.52 60 10 45591 0.42 19.25 2.95 0.52 O 1.46 22.0 249 124 4230 10 87397 1.38 120.84 2.99 0.85 45 10 63090 10.51 663.20 3.00 0.85 6010 — — 255.44 3.00 0.85 P 1.49 20.4 153 90 28 30 10 86009 0.59 50.993.25 3.50 45 10 79214 0.65 51.81 3.27 3.50 60 10 19801 2.18 43.16 3.283.50 Q 1.37 20.7 147 81 36 30 10 89662 0.33 29.20 2.94 0.40 Control - 4510 82104 0.32 26.60 2.93 0.11 Undoped 60 10 13019 3.17 41.30 2.81 −1.17NbO R — — — — — 30 10 79311 0.18 13.92 3.08 2.02 Standard - 45 10 755590.25 18.75 3.10 2.02 Undoped 60 10 45397 0.57 25.98 3.09 2.02 NbO Q wasmade on the same scale up as K-P, while R was made on a larger scale,more pure and closer to commercial grade NbO.

As listed in Table 16, the physical properties of all six new samplesare in a close, normally expected range. One significant trend however,is the BET surface area of the heat treated powder, which varied between1.32-1.72 m²/g. It appears that various dopants affect kinetics ofsintering and particle growth differently, leading to the variation infinal surface area.

As shown in FIG. 11 and listed in Table 16, the dopant oxides appear tohave significant effect on DC leakage characteristics of NbO materials.Particularly, the samples doped with Y₂O₃, SiO₂, and Mn₂O₃ showedmarkedly lower DC leakage current at high formation voltage (60V). Thedata for Y₂O₃-doped sample confirms the beneficial effect.

CV/g Vs Formation Voltage behavior for these samples is shown in FIG.12. With the exception of Mn₂O₃ doped sample, all samples possessed verylow CV/g at 60V formation. As also shown in FIG. 12, the cap roll-offbehavior is mainly dependent on primary particle size of the powder:smaller particles form away at a lower voltage than their largecounterparts.

Example 5

FIG. 13 shows the effect of donor oxides in reducing thecontaminant-driven DC leakage in NbO powders. The doped powders areprepared in lab scale attritor mill that has steel lined chamber, whichtypically contaminates the samples with Fe, Ni, and Cr. The NbO-Controlsample is made using the same equipment and process as the dopedsamples, for comparison. The NbO-Standard sample is made on Nb linedpilot scale milling equipment with reduced metallic contamination. Asseen in FIG. 13, the DC leakage behavior of the doped samples issignificantly better than the control sample. The slope of pure NbO data(Standard and Control) is markedly steeper than that of the dopedsamples. Since this technology may be applicable to Ta based capacitorpowders, it may offer a solution to control DC leakage contribution frommetallic contamination. FIG. 14 shows DC Leakage (at 60V formation) as afunction of metallic combination (Fe+Ni+Cr). The figure shows thesignificantly lowered effect of contamination in elevating DC leakage ofthe doped niobium suboxide samples.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. A niobium suboxide powder having the formula Nb_(x)O_(y) that isdoped with at least one dopant oxide, wherein x is less than 2 and y isless than 2.5× wherein said dopant oxide is an oxide of Y, Si, Mn, Al,or Ce, or any combination thereof, and said dopant oxide has a cationvalency of +2 or higher, and wherein said dopant oxide is present in anamount of from 0.25% by weight to 2.5% by weight, based on the overallweight of the powder.
 2. The niobium suboxide powder of claim 1, whereinsaid dopant oxide has an ionic size that is within 10% of an ionic sizefor niobium.
 3. A capacitor anode comprising a sintered pressed bodycomprising the niobium suboxide powder of claim
 1. 4. The capacitoranode of claim 3, wherein said capacitor anode further comprises adielectric layer without any field-induced crystallization within saiddielectric layer.
 5. The capacitor anode of claim 3, wherein saidcapacitor anode is formed with a formation voltage of from 60 volts to75 volts with a pressed density of 3.0 g/cc or higher, and sintered at atemperature of from 1000° C. to 1400° C. for 10 minutes or more at aformation temperature of 90° C.
 6. The capacitor anode of claim 5,wherein said anode has a cumulative volume of pores of greater than 1micron diameter of 0.010 mL/g or higher.
 7. The niobium suboxide powderof claim 1, wherein said dopant oxide is Y₂O₃, SiO₂, Mn₃O₄, Mn₂O₃,Al₂O₃, CeO₂, or any combination thereof.
 8. The niobium suboxide powderof claim 1, wherein said dopant oxide is Y₂O₃, SiO₂, Mn₂O₃, or anycombination thereof.
 9. The niobium suboxide powder of claim 1, whereinsaid dopant oxide is Y₂O₃, SiO₂, or any combination thereof.
 10. Theniobium suboxide powder of claim 1, wherein said dopant oxide is Y₂O₃.